ice-shoved hills and related glaciotectonic features in...

Prairie Perspectives84

Ice-shoved hills and related glaciotectonic featuresin the Glacial Lake Proven Basin, Riding Mountainuplands, Manitoba

R.A. McGinnBrandon University

Abstract: Five to six ice-shoved hills and a small composite linear ridgerepresent the suite of glaciotectonic features mapped in the Glacial LakeProven basin. The ice-shoved hills appear to be associated with smalldepression lakes located approximately 2.0 - 4.0 km upstream of a N orNE ice flow (5°-50°). The Odanah Shale member of the Pierre formationforms the core of each ice-shoved hill and approximately 1.0 m of Zelenatill overlies the shale core. Pebble clast fabric analysis from the till supportsthe hill-hole hypothesis.

The small composite linear ridge is described as a broken series ofhills 8 km long, 2 km wide and 15-30 m high. The ridge is relativelystraight and has a NNW-SSE orientation (335°). The gaps appear to begenerated by a combination of ice stagnation drainage and Holocene fluvialerosion. About 2.0 m of till overlies a deformation diamict or distortedsands and gravels. The fluvial facies contains dragfolds, overfolds andsmall thrust faults. Pebble clast fabric analysis from the upper till suggestsa northern ice flow vector (5o azimuth). A secondary vector (40o azimuth),however, supports a northeastern ice flow theory. Glacial Lake Provensediments surround the constructional glaciotectonic landforms suggestingthat they were formed during the Falconer Advance of the LostwoodGlaciation.

Introduction

Constructional glaciotectonic landforms include a variety ofhills, ridges and plains which are composed wholly or partly of

Prairie Perspectives 85

soft bedrock or drift masses that were deformed or dislocated byglacier-ice movement. (Aber 1985).

The INQUA Commission on the Formation and Properties ofGlacial Deposits, formed a Work Group on Glacial Tectonics(WGGT) in 1987. Dr. J. Aber served as the overall coordinatorfor North America. By 1993 Aber had compiled an extensivebibliography consisting of 575 entries (Aber 1993). In addition, aNorth American continental wide data base of geographic andglaciotectonic features had been constructed using the ARC/INFOsystem at the University of Regina. The WGGT (Aber et al. 1993)has classified glaciotectonics into four mappable categories:basement faults, concealed structures, ice-shoved hills and sourcebasins, the later two categories are referred to as “constructionalglaciotectonic landforms.”

Aber (1989), classified constructional glaciotectonic landformsinto five types: hill-hole pairs, large composite ridges, smallcomposite ridges, cupola-hills and flat lying mega blocks. Theseclasses represent the ideal generic types within a continuum ofglaciotectonic landforms. Intermediate, transitional and mixedfeatures also can be described (Aber 1989).

Benn and Evans employ Aber’s 1989 classification in theirtext and include descriptive examples of each constructionalglaciotectonic landform (Benn et al. 1998). The hill-hole pair isdescribed as a discrete hill of ice thrust material situated a shortdistance down-glacier from a depression of similar size and shape(Bluemle et al. 1984). Aber et al. (1993) illustrate an example ofmultiple hill-hole pairs from the Devils Lake area in North Dakota.

Composite ridges are composed of multiple slices of upthrustand contorted bedrock and or unconsolidated sediments which areoften interlayered and overlain with glaciogenic material (Benn etal. 1998). Aber (1989) subdivides these constructionalglaciotectonic landforms into small composite ridges (< 100 mrelative relief) and large composite ridges (> 100 m relative reliefand arcuate in form). Large composite thrust ridges in North Dakotaare described by Moran et al. (1980). The Brandon Hills insouthwestern Manitoba are an example of a small composite linearridge (Welsted et al. 1980: Aber 1989).


Benn et al. (1998) describe cupola-hills as glaciotectonic hillslacking a hill- hole relationship and or transverse ridge morphology.Cupola-hills have a dome-like morphology, circular to oval toelongated oval shape and are composed of deformed floes ofQuaternary sediments of older bedrock overlain by a thin carapaceof till (Bluemle et al. 1984).

Megablocks or rafts are dislocated slabs of rock andunconsolidated material transported from their original positionby glacial action (Benn et al. 1998). The Qu’appelle Valley

MANITOBA

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Figure 1: Location of the Lake Proven Basin in southwestern Manitoba.


megablock located near Esterhazy, Saskatchewan (Christianson1971) is a local example and demonstrates the susceptibility of theCretaceous Pierre Shale Formation to glaciotectonism.

Two, perhaps three, of these types of constructionalglaciotectonic landforms have been found in the Glacial LakeProven Basin, Riding Mountain Uplands, Manitoba. Otherconcealed structures including bedrock folds, faults and contortionshave been recognized in Cretaceous exposures along the ManitobaEscarpment.

The Glacial Lake Proven Basin

The Proven Lake area is located on the Riding MountainUplands south of Riding Mountain National Park, 80 km north ofBrandon, Manitoba (Figure 1). The Glacial Lake Proven basin isgenerally less than 625 m in elevation and includes present dayClear Lake, Bottle Lake, Proven Lake, Jackfish Lake and OtterLake covering an area of approximately 340 km2 (Figure 2). Higherelevations, in excess of 670 m, are located to the north and east ofthe Lake Proven Basin. The Whirlpool and Rolling Rivers drainthe southern portion of the basin towards the south; the northernportion drains to the west by way of Clear Creek (Figure 2). Bothdrainage routes join the Little Saskatchewan River, (Klassen’sancestral Minnedosa River) and eventually drain into theAssiniboine River to the south.

Detailed surficial mapping (Klassen 1966, 1979; McGinn 1991,1997) have determined that early Glacial Lake Proven depositsoccur at elevations above 625 m in the region to the west andsouthwest of the topographic basin (Figure 3). These rhythmitedeposits represent a supraglacial thermokarst lacustrine facies. Thedeposits of the later phase of Glacial Lake Proven are believed torepresent a topographically controlled terminoglacial lacustrinefacies, perhaps supraglacial, but with only a thin ice base. To thewest are the deposits of the eastern ridge of the Horod Moraine, anice marginal ridge associated with the general stagnation ofWisconsinan Ice on the Eastern Uplands (McGinn 1997). This


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Figure 2: Topography of the Lake Proven Basin.


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Figure 3: Surficial deposits in the Glacial Lake Proven Basin.


landform delimits part of the western shoreline of early Glacial LakeProven (Figure 3).

To the north, a glaciofluvial facies (proglacial outwash) mergeswith constructional glaciotectonic features in the east. It is theseconstructional glaciotectonic landforms that are the topic of thispaper. The suite of landforms include: two small oval shaped hillsin the south (OH), a large elongate oval ridge (EOR), three othersmaller elongate oval shaped hills (EOH) and an 8 km longsegmented ridge centred on the town of Onanole (Figure 4).

Ice- Shoved Hills

The two southern ice-shoved hills (OH) are oval in form,approximately 0.75 km in diameter and 10 m - 15 m high. Thenorthern ice shoved hills (EOH) are elongated but do not displayarcuate form. These hills are generally larger, 2.0 km - 3.5 km inlength, 0.25 km -1.0 km wide, display 10 m -15 m relative reliefand are aligned along a north-south vector (350° azimuth).

A large elongated oval ridge (EOR) is situated north ofErickson, east of Provincial Highway 10 and approximately halfway between the southern ice-shoved oval hills and the morenorthern elongated oval hills (Figure 4). This ice-shoved elongatedoval ridge is 7.0 km long and 2.3 km wide. The feature isapproximately 15 m in relative relief except for a prominent domeshaped hill located near the southern end, which stands 45 m abovethe Glacial Lake Proven plain.

The two oval shaped hills and the large elongated oval ridge(EOR) north of Erickson appear to be associated with smalldepression lakes located approximately 2.0 km upstream of iceflow directions (40°-50° azimuth) (Figure 5). The other threeelongated oval hills may be related to depression lakes 4.0 kmupstream (azimuth 0°-20°) (Figure 5).

The hill-hole pairs (Figures 4 and 5) are composed of the OdanahShale member of the Pierre formation. Odanah Shale is describedas hard olive-grey siliceous shale with soft interbeds of darker olive-grey shale. The shales are composed of clay sized siliceous particleswhich show no sign of biogenic origin (McNeil et al. 1981). The


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Figure 4: Topography of constructional glaciotectonic landforms in theGlacial Lake Proven Basin.


Proven

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Location: Beatty Pit

Material: Upper facies - Zelena Till

Figure 5: Glacial Lake Proven Basin hill-hole pairs.


mineralogy is described as amorphous silica and illite with traces ofquartz and organic carbon (Bannatyne 1959). Roadcut exposuresin the small oval hill just north of Erickson indicate that the strike isgenerally as expected, however, dips appear to be disrupted andplunge opposite the acknowledged trend.

Approximately 1.0 m of Zelena till overlies the shale core.The Zelena formation, on average, is 3.0 m - 5.0 m thick in theregion and represents the uppermost tills and intertill sediments onthe Riding Mountain Uplands. Klassen (1979) suggests that theZelena formation was deposited during the final stages of glacialstagnation during the Late Wisconsinan. Oxidized Zelena till isusually yellowish brown or very dark grey brown in colour. Fresh(unoxidized) exposures are dark olive grey or very dark grey(Klassen 1979). The till is shale rich but since Pierre Shale claststend to disintegrate when removed from the matrix, it is difficult todetermine a percentage composition. Carbonates constituteapproximately 26% - 36% of the clasts (Klassen 1979).

Stratigraphic exposures in the Erickson Pit (Figure 5) locatedadjacent to the southernmost hill-hole pair reveal two tills overlyingdeformed sands and gravel. The upper diamict, described as asupraglacial meltout complex (Brodzikowski and van Loon, 1991),overlies a slightly more compact supraglacial ablation till. Themeltout complex is usually a typical diamict, massive in appearancebut with occasional concentrations of relatively coarse or finematerial forming vague lenses. The ablation till is massive, andslightly more compact. The prominent clasts are typically Interlakecarbonates as the local Odanah Shale clasts quickly achieve terminalgrade. Larger shale clasts are evident but difficult to remove withoutfracture. The underlying fluvial facies (proglacial outwash) containsshearing flexures and small thrust faults, which supports aglaciotectonic modification. Unfortunately, the Erickson Pit wasreclaimed before pebble clast fabric analysis was undertaken.Pebble clast fabric analysis from the till exposures towards thenorth, however, support the hill-hole hypothesis illustrated in Figure 5.


Small Composite Linear Ridge

Associated with the ice shoved hill-hole pairs is a low reliefridge, centred on Onanole, Manitoba (Figure 4). This smallcomposite linear ridge is described as a broken series of hills 8.0km long, 2.0 km wide and 15 m -30 m high. The gaps appear to begenerated by a combination of ice stagnation drainage and Holocenefluvial erosion.

The ridge may be divided into a NNW-SSE orientation (335°)tri-sectional ridge (CLR) and two distal outlier hills (O) (Figure4). The tri-sectional ridge is slightly arcuate, suggesting an iceadvance from the northeast.

An alternate interpretation employs a natural drainage channelto divide the landform into a northern suite (two sections of theridge and a northern outlier) and a southern unit composed of acontiguous ridge section and outlier (Figure 4). The northern hillstypically exhibit 15 m - 20 m relative relief. The southern unit ishigher and broader.

Ice proximal sections in the Beatty Pit (Figure 4) expose about2.0 m of till overlying a deformation diamict and/or distorted sandsand gravels. The fluvial facies contains dragfolds, overfolds andsmall thrust faults. The deformation diamict, in places, ispredominantly reworked coarse glaciofluvial material. When thisis the case, dragfolds, overfolds and crenulations are common.When the deformation diamict is reworked till, shear flexures andsmall thrust faults occur. Pebble clast fabric analysis (Figure 5)from the upper till suggests a northern ice flow vector (5o azimuth).A secondary vector (40o azimuth), however, supports thenortheastern ice flow theory.

North of Onanole discordant shale bedrock is exposed in asmall borrow pit on the proximal side of the ridge. At this site thestrike appears to be as expected, apparent dips seem to be disrupted,plunging opposite the acknowledged trend.

Conclusions

One might suggest that these hypothesized ice shoved hills arein fact shale bedrock subcrops. Perhaps subsurface drilling could


resolve the conflict, but that is unlikely to occur. The stratigraphicevidence (tills over deformed glaciofluvial material) in both thesurrounding ice stagnation plain and the Small Composite LinearRidge support the conclusion that these features are Cupola-Hillsand perhaps Hill-Hole Pairs.

All appear to have formed during the Falconer Advance of theLostwood Glaciation and are surrounded by Glacial Lake Provensediments. The fluvial facies appears to be outwash suggestingthe glacier advanced over its outwash plain. Subglacial shear andfolding were probably aided by porewater pressure and frictionaldrag.

References:

ABER, J. 1985 “The character of glaciotectonism” Geologie en Mijnbouw64: 389-395

ABER, J. 1988 “Ice-shoved hills of Saskatchewan compared withMississippi Delta mudlumps – Implications for glaciotectonic models”Croot, D. (ed) Glaciotectonics Forms and Processes Rotterdam:Balkama 1-9

ABER, J. 1989 “Spectrum of constructional glaciotectonic landforms”Goldthwait, R. and Matsch, C. (eds) Genetic Classification ofGlacigenic Deposits Rotterdam: Balkema 281-292

ABER, J. 1993 “Expanded Bibliography of Glaciotectonic References”Aber, J. (ed) Glaciotectonics and Mapping Glacial Deposits Regina:Canadian Plains Research Center 99-137

ABER, J., BLUEMLE, J., DREDGE, L., SAUCHYN, D. andACKERMAN, D. 1993 “Glaciotectonic Data Base and Mapping ofNorth America” Aber, J. (ed) Glaciotectonics and Mapping GlacialDeposits Regina: Canadian Plains Research Center 177-200

BANNATYNE, B. 1970 “The clays and shales of Manitoba” ManitobaDepartment of Mines and Natural Resources, Mines Branch,Publication 67(1): 1-104

BENN, D. and EVANS, D. 1998 Glaciers and Glaciation London: ArnoldBluemle, J. and Clayton, L. 1984 “Large scale glacial thrusting andrelated processes in North Dakota” Boreas 13: 279-299

CHRISTIANSON, E. 1971 “Geology and groundwater resources of theMelville Area (62 k, l) Saskatchewan” Saskatchewan ResearchCouncil, Geology Division, Map 12


KLASSEN, R. 1966 “Surficial geology of the Riding Mountain area,Manitoba-Saskatchewan” Unpublished Ph.D. Thesis Saskatoon:University of Saskatchewan

KLASSEN, R. 1979 “Pleistocene Geology and Geomorphology of theRiding Mountain and Duck Mountain areas, Manitoba-Saskatchewan”Geological Survey of Canada Memoir 396: 1-52

McGINN, R. 1991 “The formation and draining of late Wisconsinansuperglacial lakes on the Riding Mountain Uplands, Manitoba”Atlantic Geology 27: 221-227

McGINN, R. 1997 “The Horod Moraine: The facies and deposits of asupra-terminoglacial subenvironment” Thraves, B., Paul A. andWiddis, R. (eds) The Estevan Papers. Regina Geographical Studies,6. Regina: 100-112

MORAN, S., CLAYTON, L., HOOKE, R., FENTON. M. andANDRIASHEK, L. 1980 “Glacier-bed landforms of the PrairieRegion of North America” Journal of Glaciology 25(93): 457-476

McNEIL, D. and CALDWELL, W. 1981 “Cretaceous rocks and theirforamifera in the Manitoba Escarpment” Geological Association ofCanada Special Paper 21: 1-439

WELSTED, J. and YOUNG, H. 1980 “Geology and origin of the BrandonHills, southwest Manitoba” Canadian Journal of Earth Sciences 17:942-951

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